1. Field of the Invention
The present invention relates to a lubricated aromatic polyester copolymer composition which is used for molding in an automatic releasing system.
2. Description of the Prior Art
Aromatic polyester copolymers obtained from terephthalic acid and isophthalic acid or functional derivatives thereof and bisphenol or a functional derivative thereof have been known.
As the processes for producing such aromatic polyester copolymer, the following processes have been known. An interfacial polymerization for mixing a solution of terephthalic acid dichloride and isophthalic acid dichloride in water immiscible organic solvent with a solution of a bisphenol in an alkaline aqueous solution to react them. A solution polymerization for reacting terephthalic acid dichloride and isophthalic acid dichloride with a bisphenol in an organic solvent. A melt polymerization for heating terephthalic acid and isophthalic acid with a bisphenol in the presence of acetic anhydride. A melt polymerization for heating phenyl esters of terephthalic acid and isophthalic acid with a bisphenol. A melt polymerization for heating terephthalic acid and isophthalic acid with a bisphenol in the presence of diallyl carbonate.
It is well-known that the resulting aromatic polyester copolymers have excellent characteristics such as excellent mechanical characteristics of tensile strength, bending strength, bending recovery coefficient and impact strength; excellent thermal characteristics of thermal deformation temperature and thermal decomposition; excellent electric characteristics of inherent resistance, insulation withstand, arc resistance, dielectric constant and dielectric loss; excellent fireproof property; excellent dimensional stability and excellent chemical resistance. Therefore, various applications can be considered for molded products, films, fibers and coated products of the copolymers obtained by an injection molding process, an extrusion molding process, a press molding process or various molding processes.
The aromatic polyester copolymers have excellent mechanical characteristics, electric characteristics, heat resistance and dimensional stability whereby the copolymers can be used for various productions of parts of precision machines and electric parts. Recently, automatic processes and energy saving processes in molding and processing of synthetic resins have been studied, especially various processes for automatic demolding of molded products have been developed, since synthetic resins have been used in a large quantity for parts of precision machines, electric parts and miscellaneous goods. The molded products must have nontackiness to the molds and less resistance in the demolding of the molded products in order to operate smoothly the automatic demolding machines. If the resistance in the demolding is great, the molded products may be deformed or damaged by the mechanical force to cause inferior value of goods. Sometimes, the molded products or the molds especially a projecting mechanism may be damaged. In order to reduce the resistance in the demolding, it has been considered to form a slant for demolding in the mold or to coat a releasing agent. In the molding of parts of precision machines or electric parts which require dimensional stability or the molding of molded products having complex configuration, the slant for demolding may not be given. In the molding of molded parts having certain configuration, a projecting mechanism especially a size and position of a projection pin is remarkably limited. Therefore, a releasing agent has been often used for improving demoldability. When excess of the releasing agent is coated, however, an appearance of the molded product may be inferior and a weld strength may be reduced to cause serious disadvantages that the characteristics of the resins can not be imparted.
It is important to improve the demoldability of the aromatic polyester copolymers having excellent characteristics for parts of precision machines and electric parts in view of the production of molded products having excellent original characteristics of the aromatic polyester copolymers.
A lubricant has been usually incorporated into a resin to improve demoldability of molded products. The effects of the lubricant are to reduce internal friction of the resin so as to improve the fluidity (internal lubricating effect) and to improve lubricating effect at an interface between the resin and the mold (external lubricating effect).
In order to improve the internal lubricating effect, a lubricant having high miscibility to the resin is usually used. In order to improve the external lubricating effect, a lubricant having low miscibility to the resin is usually used. However, mechanical characteristics and thermal characteristics are often deteriorated by the addition of a lubricant to resins.
It has been proposed to incorporate polyethylene or polypropylene especially low molecular weight polyethylene or polypropylene into the aromatic polyester copolymer so as to improve processability (internal lubricating characteristic) (Japanese Unexamined Patent Publication No. 71035/1974) or to improve demoldability (external lubricating characteristic) (Japanese Unexamined Patent Publication No. 3456/1975) without deterioration of the original mechanical characteristics and electric characteristics of the aromatic polyester copolymer. When polyethylene or polypropylene is incorporated into the aromatic polyester copolymer, cloud, devitrification or opaque of the molded product has been caused. The applications of the molded products have been disadvantageously limited in the fields for requiring transparency of the molded products.